1. Field of the Invention
The present invention relates to a multifunctional back layer for photographic elements.
2. Brief Description of the Background of the Invention Including Prior Art
In general, photographic elements consist of a support material and the photographic layers. Support materials are provided with one or more additional layers on their back in order to prevent, for example a curl or an accumulation of electrostatic charges on the surface during the processing of the material, i.e. during the wetting and casting with light-sensitive emulsions or also after the passage through the processing solutions during the sorting processes.
In addition to the recited antistatic properties, the back side layer of the photographic material is to meet simultaneously the following requirements:
(1) Low dirt reception during passage of the photographic material through roller-transport developing machines, where dirt films of the oxidation product of the developer deposit easily. PA1 (2) An abrasion strength which is a high as possible and a stability in alkaline developer solutions which, for example, is important in the passage of the photographic material through a processing machine operating with rollers. PA1 (3) Good printability during printing with conventional printing inks as well as good lettering capability. PA1 (4) Good adhesive-tape adhesion since, during the passage of the photographic material through modern automatic developing machines, in each case, the next following roll is glued or adhesively attached to the preceding roll, and the adhesive attachment has to be assured during the passage of the adhesively attached junction through the developer processing solutions. PA1 a colloidal surface-hydroxylated aluminum-modified silica, PA1 an alkali-metal salt of an organic polysulfonic acid or an organic polysulfate, PA1 an aqueous dispersion of a copolymer of at least three components and forming an acrylic-acid-alkyl-ester with a content in free carboxylic groups of from about 1-10 mole-% and in free hydroxy groups of from about 5-20 mole-%, and wherein the sum of free carboxylic groups and hydroxy groups does not exceed 25 mole-%, and PA1 a trifunctional aziridine as a cross-linking agent.
It is very difficult in practice to obtain these properties simultaneously, since the components known for such purpose influence the material properties in part in opposite ways. Hydrophobic components, for example, are associated with the disadvantage of a high acception for dirt and low antistatic effectiveness, while hydrophilic components result in a low adhesive-type attachment, poor printability, and insufficient strength in the processing solutions.
It is known that the static charting of the back side layer can be reduced by matting and dulling agents. Thereby, the adhesion of two photographic materials on one another is reduced. Furthermore, it is known that the already present static charging can be removed by incorporating electrically-conducting additives in the layer.
For example, photographic material with the silver halide emulsion layer on one side of a polyolefine-coated photographic support material and with another antistatic layer on the opposite side of the photographic support material is known from the U.S. Pat. No. 4,582,783, where the antistatic layer contains a sodium-magnesium silicate, a sodium-polystyrene-sulfonate, and certain succinic-acid-semi-esters. The conductivity of this combination is such that desired antistatic properties are sufficient. In addition, the material also exhibits a relatively low dirt acceptance. However, this is associated with losses relating to the other required properties.
Materials showing antistatic properties are in general soluble in water due to their ionic conductivity, or at least can swell in water. Thus, a good conductivity usually results in a bad adhesion of the layer during passage through the processing solutions. The good conductivity is associated with a reduced abrasion strength as well as a poorer adhesive-tape adhesion.
It is difficult in principle to obtain a photographic material which corresponds, with respect to all five properties recited above, to the requirements. Polar surfaces are in fact conductive (antistatic property) and exhibit a low reception for dirt, but with increasing polarity, the abrasion strength and the adhesive-tape adhesion decrease as a result of the processing solution's influence. On the other hand, an improvement of the adhesive-tape has led hitherto to conductivity decreases and to increased dirt acception to the photographic material.